A vehicle speed control system adjusts the position of an engine throttle plate in order to maintain a driver selected speed (the SET speed). At the moment that the driver starts automatic speed control, the control system reopens the throttle and takes over the vehicle operation.
The control action typically consists of two components: 1) the desired initial servo motor position; and 2) the control algorithm for providing adjustments according to speed errors. For the first component, the required servo motor position is derived from the SET speed through a linear approximation. In order to find a good approximation for different speed ranges for various vehicle models, this linear approximation is calibrated with many tradeoff considerations between high speed and low speed, many hours of test driving, and calibration experience for fine tuning. Additionally, the control algorithm in the second component contents with the nonlinear response of the engine dynamics and the vehicle dynamics, which leads to a complicated control system design and calibration process.
Thus, there exists a need for accurately determining the desired initial servo motor position considering the nonlinear properties of the vehicle, and for modifying this initial servo motor position in real time to accommodate various operation conditions.